System and method for the production of gypsum board using starch pellets

ABSTRACT

The present invention relates to a system and method for the production of gypsum board using starch pellets. In accordance with the present disclosure, the starch necessary for board formation is provided in the form of starch pellets. These pellets are mixed with a gypsum slurry in a mixer. The pellets are initially insoluble and do not dissolve. However, during subsequent drying stages, the pellets become soluble and dissolve into the gypsum phase. This both provides the desired starch component and also results in the formation of voids within the set gypsum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to applicationSer. No. 14/537,646 filed Nov. 10, 2014, and entitled “System and Methodfor the Production of Gypsum Board Using Starch Pellets,” which is acontinuation of and claims priority to application Ser. No. 13/232,513,filed on Sep. 14, 2011, and entitled “System and Method for theProduction of Gypsum Board Using Starch Pellets,” now U.S. Pat. No.8,882,943. The contents of these applications are fully incorporatedherein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to the production of gypsum board. Moreparticularly, the present invention relates to the use of foamed starchpellets in the production of lightweight gypsum board.

Description of the Background Art

Gypsum board is one of the most widely used and versatile buildingmaterials in the world. The general construction of gypsum boardincludes a core of calcium sulfate dihydrate that is sandwiched betweenopposing paper sheets. The core is initially deposited in the form of aslurry; namely, calcium sulfate hemihydrate (CaSO₄.½H₂O) in water. Oncethe slurry is deposited, it is rehydrated to form gypsum. Thehemihydrate is initially prepared in a mill via the following reaction:CaSO₄.2H₂O+heat→CaSO₄.½H₂O+1½H₂O (steam)

The dehydrated calcium sulfate is known as calcined gypsum, stucco, orplaster of Paris. Gypsum has a number of desirable physical propertiesthat make it suitable for use as a building material. These propertiesinclude fire resistance, compressive strength and neutral pH. Gypsum isalso a beneficial building material because it can be formed intovarious shapes and is inexpensive and plentiful.

It is also known in the art to use additives with gypsum. One suchadditive is starch. Starch can be added prior to rehydration. Starchfunctions as a binder within a set gypsum and yields boards with highercompressive and flexural strength. It also strengthens the edges of theresulting board and improves paper bond to the core.

It is further known in the art to form voids with the interior of gypsumboard as a means for reducing the board weight. The background artincludes several examples of void formation. One technique is describedin U.S. Pat. No. 6,706,128 to Sethuraman. Sethuraman '128 discloses amethod for adding air bubbles of different relative stabilities, wherebythe air bubbles do not rupture before the slurry sets sufficiently toprevent the slurry from filing the void spaces left behind by rupturedbubbles. The result is a gypsum board with reduced weight.

Another example is illustrated in U.S. Pat. No. 1,776,325 to Robinson.Robinson '325 discloses a method of making a cellular wall board byincorporating an aerated starch into a slurry. As a result of theaerated starch, the slurry is given a desired porosity and forms acellular core.

Finally, U.S. Pat. No. 5,643,510 to Sucech discloses a method forproducing foamed gypsum board using a foaming agent blend. The ratiobetween a first and second foaming agent are controlled to adjust thesizes of foam voids within a gypsum core.

Although each of the above referenced inventions achieves its individualobjective, they all suffer from common drawbacks. Namely, the voids areformed via the use of foaming agents require additional chemicals to beadded to the gypsum. Void formation added via aeration likewise requiresadditional machinery. Moreover, in both methods the control of theassociated machinery is difficult. In prior methods of void formation itis also difficult to form voids of the correct size.

SUMMARY OF THE INVENTION

One of the advantages of the disclosed method is that it results in voidformation within gypsum building board.

Another advantage is that void formation can be increased without addingadditional foaming agents.

Still yet another advantage is that void size can be controlled and/orspecified.

Still another advantage is that the disclosed pellets provide thedesired starch component to the board while at the same time providingvoids within the core.

Another advantage is that the provided starch enhances the wallstructure of the voids that are created upon the dissolution of thestarch, as a fraction of the starch is retained at the void/solidinterface.

Yet another advantage of the disclosed system and method is that itprovides for the production of gypsum board that is both strong andlightweight.

These and other advantages are accomplished by a system and method thatinvolves providing a mixture of stucco and foamed starch beads along aboard production line. The starch pellets are slightly soluble attemperatures below 140° F. The stucco/foamed beads slurry is thendeposited between opposing sheets to form a composite panel. The set wetboard is then transferred to a dryer. Dryers are then used to dry thepanel. The heating causes the starch to dissolve, whereby the dissolvedbeads provide starch to the gypsum core and/or bond area of the paper.The dissolving beads also create a fairly uniform bubble structurewithin the core. The pellets thereby produce voids within the set board.

The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription of the invention that follows may be better understood sothat the present contribution to the art can be more fully appreciated.Additional features of the invention will be described hereinafter whichform the subject of the claims of the invention. It should beappreciated by those skilled in the art that the conception and thespecific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is a flow chart illustrating the steps associated with thedisclosed method.

FIG. 2 is an elevational view of a board production line.

FIG. 3A is a sectional view of a board taken from FIG. 2.

FIG. 3B is a sectional view of a board taken from FIG. 5.

FIG. 4 is an elevational view of the entrance to a board dryer.

FIG. 5 is an elevational view of the exit from a board dryer.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to a system and method for the productionof gypsum board using foamed starch beads. In accordance with thepresent disclosure, the starch needed for preferred board formation isprovided in the form of individual foamed beads. These beads aredispersed within a gypsum slurry by way of a mixer. The pellets areinitially insoluble and do not dissolve in the presence of the gypsumslurry. However, during subsequent heating in a dryer, the beads becomesoluble and dissolve into the gypsum phase. This dissolution providesthe desired starch component to the gypsum while at the same timeproducing voids within the core.

The preferred starch beads, or pellets, are formed by way of anextrusion process. During the process, air is combined with starch viaan extruder. The resulting foamed pellets may be of an irregular sizebut generally have a diameter of between approximately 1/32 of an inchto 1/64 of an inch. A mix of different sized pellets can also be used.Other sizes can be produced depending upon the parameters of theextruder. Other processes can likewise be used for formation of thefoamed starch pellets. For example, the pellets can be formed via knownprilling processes. They can also be made into droplets similar topolystyrene manufacturing methods. In the preferred embodiment, thefoamed pellets are hydrophobic at low temperatures and resist dissolvingat temperatures below approximately 140° F.

FIG. 1 is a flow chart illustrating the steps carried out in accordancewith the present disclosure. In the first step 20, the foamed pelletsare combined with stucco. In the preferred embodiment, the pellets makeup between approximately 5 to 50% of the overall slurry by volume.Preferably, the pellets and stucco are combined prior to the mixer.

At step 22, the pellets and stucco are mixed with water in a mixer tocreate a slurry. The mixer can be a conventional mixer typically foundin board production lines. This blending step fully encapsulates thepellets within the resulting slurry. Again, however, the pellets remaininsoluble at this point and the starch is not dissolved into the gypsumphase. The blended slurry is then deposited between opposing papersheets to form a panel at step 24.

The panel with the slurry and encapsulated pellets are then dried in aseries of dryers at step 26. As the panel is dried, and the temperatureof the board approaches 200° F., the pellets become soluble and dissolveinto the gypsum phase as starch. The dissolved pellets leave behindvoids within the board. The panel dries simultaneously with the starchdissolution. The result, as noted at step 28, is a set gypsum board thatcontains both the desired amount of starch and that has voids to reducethe weight of the board.

The system of the present disclosure is carried out along a boardproduction line 32 as noted in FIG. 2. A suitable product line is morefully described in commonly owned U.S. Pat. No. 6,524,679 to Hauber, thecontents of which are fully incorporated herein. Production line 32generally includes a mixer 34 with various outlets 34 a, 34 b, and 34 c.These outlets can deposit slurry in varying densities in order to form acore with varying physical properties. Supplies of foamed pellets andstucco are also included (36 and 38, respectively). These supplies feedinto a container 42 where the pellets and stucco are initially combined.In the preferred embodiment, the foamed pellets and stucco are mixedwhile dry. Water is subsequently added at mixer 34 to form a slurry andbegin the re-hydration process. As noted, the pellets and slurry arepreferably combined at a ratio of between approximately 5-50% by volume.

Container 42, in turn, feeds into mixer 34. This can be a conventionalmixer currently used in a gypsum board manufacture. As noted, mixer 34is used in blending the pellets and stucco with water. This blendingconverts the stucco to slurry and ensures that the individual pelletsare encapsulated by slurry. Additional additives can be added to themixer as needed depending upon the requirements of the gypsum board.

The production line further includes two or more large wound rolls ofpaper 44. In one embodiment, two rolls are included for forming theupper and lower paper sheets (46 and 48, respectively) of the gypsumboard 52. Additional rolls can be provided for including fibrous mats orother sheets depending upon the intended use of the resulting board.Mixer 34 deposits the gypsum slurry between sheets 46 and 48 upon aforming table 54. The majority of the slurry is preferably dispensed atoutlet 34 b. If desired, a small amount of denser slurry can be appliedto bottom paper sheet 46 at outlet 34 a. A denser slurry can likewise beapplied to upper paper sheet at outlet 34 c. Outlets 34 a, 34 b, and 34c can all deliver blended slurry with pellets from mixer 34.Alternatively, the blended gypsum with pellets can be limited to outlet34 b, with outlets 34 a and 34 c supplying gypsum slurry withoutpellets.

In either alternative, top sheet 48 is applied over the deposited gypsumwith blended pellets immediately prior to a pinch point 56. Thereafter,the resulting panel 52 is passed through a hinge plate 58 and extrusionplate 62 to ensure that the panel 52 as the desired thickness. Withreference now again to FIG. 3A, it is seen that following extruder 62, apanel 52 is a composite that includes a bottom paper sheet 46, theblended gypsum core 64 with encapsulated pellets 66, and a top papersheet 48. Moreover, the individual foamed pellets 66 are distributedthroughout the thickness of the gypsum core 64. At this stage, thepellets are undissolved, only slightly soluble, and fully encased withinthe core 64 of unset slurry. Prior to entering the board dryers 68, thegypsum core sets in accordance with the following equation:CaSO₄.½H₂O+1½H₂O→CaSO₄.2 H₂O

Thereafter, the composite panel is cut into desired lengths at cuttingstations (not shown) and then delivered via belts to a series of boarddryers 68. FIG. 4 illustrates the composite panels being delivered tothe entrance of board dryer 68, whereas FIG. 5 illustrates the compositepanels exiting board dryer 68. During the drying phase, the panel isexposed to temperatures in excess of 140° F. and generally in theneighborhood of 200° F. As is known in the art, the dryers 68 are usedto dry the gypsum slurry. However, in accordance with the presentdisclosure, the excess temperatures also cause the individual pellets 66encapsulated within the gypsum to become very soluble. After becomingsoluble, pellets dissolve 66 whereby the starch is dissolved into thegypsum phase of core 64. This starch, when combined with the gypsum,provides the necessary degree of board strength and can also improve thebond between the facing paper and the core.

Upon dissolving, the individual foamed pellets 66 leave behind voids 72which, like pellets 66, are distributed throughout the thickness of theset gypsum core 64 (note FIG. 3B). The result is a gypsum building panel52 with a core 64 of set gypsum. This set gypsum has the needed starchby virtue of the dissolution of the foamed pellets 66. Additionally,voids 72 that are left behind function to both reduce the overall weightof panel 52 and provide added strength. Each individual void alsoincludes a peripheral lining. The starch dissolution is such that thestarch concentration is higher at the void lining than in the remainingcore body.

The present disclosure includes that contained in the appended claims,as well as that of the foregoing description. Although this inventionhas been described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

What is claimed is:
 1. A method of producing lightweight gypsum board,the method utilizing a board production line including a mixer, aforming table, and dryers, the method comprising: providing a pluralityof starch pellets, the pellets being of a uniform size and being onlyslightly soluble at temperatures below approximately 140° F., thepellets being more soluble at elevated temperatures; adding the pelletsto a gypsum slurry in a pellet to gypsum ratio of between approximately5/100 to 50/100 by volume; blending the gypsum slurry and pellets withinthe mixer whereby the pellets become fully encapsulated within theslurry; supplying a first facing sheet to the forming table prior to themixer; discharging the blended gypsum and pellets from the mixer andonto the first facing sheet; supplying a top facing sheet over theblended gypsum and pellets to form a composite panel; drying thecomposite panel within the dryers to a temperature in excess ofapproximately 140° F., the drying causing the pellets to dissolve andthe residual moisture to be removed from the board, whereby thedissolved pellets provide starch to the gypsum slurry and create voidswithin the set gypsum.
 2. The method as described in claim 1 comprisingthe further step of combining air and starch to form the starch pellets.3. A method of producing building board, the method utilizing starch,stucco, and water, the method comprising: combining the starch with airto form starch pellets, the pellets being slightly soluble attemperatures below approximately 140° F.; mixing the starch pellets withthe stucco and the water to form a slurry, with the mixing serving tofully encapsulate the pellets within the slurry; dispensing the slurrybetween opposing sheets to form a composite panel; drying the compositepanel, the drying causing the pellets to dissolve and the slurry to set,whereby the dissolved pellets provide starch to the slurry and createvoids within the set slurry.
 4. The method as described in claim 3wherein the pellet to stucco ratio is between 5/100 to 50/100 by volume.5. The method as described in claim 3 wherein the pellets are formed viaan extrusion or other foaming procedure.
 6. The method as described inclaim 3 wherein the pellets are hydrophobic at temperatures belowapproximately 140° F.
 7. The method as described in claim 3 wherein thepellets are formed from an ethylated starch.
 8. The method as describedin claim 3 wherein the starch pellets are formed via a prilling process.9. A method of producing a gypsum board having opposing sheets and acore with voids, the method comprising: providing a volume of gypsumslurry; providing an amount of starch; mixing the starch with air andwater; drying the mixture to form a number of dry starch pellets; addingthe starch pellets to the gypsum slurry; mixing the starch pellets withthe slurry to fully encapsulate the pellets; depositing the starchpellet and slurry mixture between the opposing sheets; drying the slurryto dissolve the starch pellets and create the voids within the core, thedissolved starch pellets providing a concentration of starch within thegypsum board.
 10. The method as described in claim 9 wherein the voidsinclude a lining and wherein the concentration of the dissolved starchis higher at the void lining than in the core body, whereby the voidlining is strengthened and the resulting board is likewise strengthened.11. The method as described in claim 9 wherein the pellets have anapproximate particle size that is greater than 800 microns.
 12. Themethod as described in claim 9 wherein the pellets have an approximateparticle size that is less than 400 microns.
 13. The method as describedin claim 9 wherein the dissolved starch pellets yield a uniform bubblestructure within core, thereby strengthening the core.
 14. The method asdescribed in claim 9 wherein the pellets and stucco are combined at aratio of between 5/100 to 50/100 by volume.
 15. The method as describedin claim 9 including the additional step of forming the pellets via anextrusion process.
 16. The method as described in claim 9 wherein thepellets are hydrophobic at temperatures below approximately 140° F. 17.The method as described in claim 9 comprising the further step offorming the pellets from an ethylated starch.
 18. The method asdescribed in claim 3 wherein the voids include a lining and wherein theconcentration of the dissolved starch is higher at the void lining thanin the core body, whereby the void lining is strengthened and theresulting board is likewise strengthened.